Technical Field
This application relates to an ultrasound system and method for determining density.
Background of Related Art
Cerebrovascular disease refers to diseases of the brain caused by vascular abnormalities which result in abnormal cerebral blood flow. The most common cause of cerebrovascular disease is narrowing of the major arteries supplying blood to the brain, resulting in thrombogenic disease or sudden occlusion of blood flow, which if large enough results in ischemic stroke.
Clots (Ischemic Stroke) can originate in various areas and be caused by different modalities. These different modalities create clots that vary in consistency. The clot can be platelet rich (runny) or fibrin rich (hard) or anywhere in between the two. Ischemic stroke is caused by the thrombosis of a major vessel supplying blood to a region of the brain. A shortage of blood in the cerebral tissue leads to the deletion of metabolites such as oxygen and glucose, which in turn causes depletion of energy stores of the cells. Therefore, it is critical to remove the clots to restore adequate blood supply to the brain.
Current treatments for clot removal include application of thrombolytic drugs to dissolve the clot, aspiration, and mechanical thrombectomy devices in minimally invasive procedures. A problem encountered with these approaches is that the composition of the clot is undetectable in situ, while the efficacy of these approaches is dependent in part on the clot composition. Therefore, the physician is taking one of the known approaches for treatment of the clot without the knowledge of the clot makeup, e.g., its consistency. This can lead to inconsistent results as well as failure to properly treat the clot.
It would therefore be beneficial if the surgeon could identify the type of clot beforehand to better assess how the clot could be treated. Such prior knowledge would greatly enhance clot removal as the surgeon can adapt the approach to better match the treatment device or drugs with the type of clot.
Although techniques for identifying characteristics of blood clots are known, the need exists for a simple, reliable, easy to use and low profile system for clot assessment. It would also be beneficial to provide such system which can effectively assess blood clot characteristics at various times during the procedure.
Moreover, in addition to determining the type of blood clot, it would also be beneficial to assess whether the blood clot has been effectively removed during the procedure without relying on current methods, such as injecting contrast, which can have adverse effects such as re-compacting the clot.
In addition, in cerebrovascular disease, the vitality of the vasculature distal to the clot is compromised once the clot lodges in place. Vasculature that has been deprived of oxygenated blood will necrose and become friable. Once blood flow is restored after clot removal, such blood flow could potentially cause a hemorrhagic event, which means the vessel can bleed out and burst open. Currently, surgeons do not have adequate knowledge of the vasculature downstream of the clot and therefore cannot accurately assess the risk of clot removal by for example dissolution, aspiration or mechanical thrombectomy.
It would be beneficial if the surgeon could determine the health of the vasculature distal to the clot prior to removal of the clot so the surgeon could determine if clot removal is advisable and/or take necessary precautions during clot removal so the vessels are not compromised. Prior attempts to measure pH using magnetic resonance imaging (MRI) technique have been attempted, as explained for example in “Modelling of pH Dynamics in Brain Cells After Stroke”, by Piotr Orlowski, et al., published in Interface Focus, The Royal Society, 2011. However, these attempts to date have been unsuccessful. Additionally, relying on MRI is very expensive and requires relatively complex mathematical models. Further, an ischemic event might need to be treated in an ambulance prior to arrival at a hospital and thus an MRI is not possible. Therefore, although the role of pH of the vasculature is recognized, the need exists to utilize this parameter to readily and inexpensively determine in hospital and non-hospital settings vascular tissue health to enhance blood clot removal or prevent clot removal where the risk is too great. This would provide great benefits not only for hospital treatment but for pre-hospital treatment such as in the ambulance or home prior to arrival at the hospital.
Additionally, after assessment of the health of the vasculature and selection of the proper clot treatment, it might be beneficial to control the restoration of blood flow. Being able to determine the health of the vasculature would thus advantageously enable gradual return of blood flow if deemed necessary to reduce the risk of hemorrhaging.